The Weeds Response to the Winter Vetch (Vicia villosa) and Chicklingpea (Lathyrus sativus) Cover Crops under Different Tillage Methods in Corn Fields

Using cover crops in conservation tillage systems offers many advantages, one of which is weed control through physical and chemical interferences. Most of the benefits of cover crops are well known. They prevent form wind and water erosions, conserve soil moisture by reducing evaporation and increasing infiltration, increase the content of organic matter, increase fertility by recycling nutrients, add nitrogen if they are legumes, and improve soil structure. Proper cover crops can also suppress weed growth by allelopathic activities and light interference. They impact on environmental quality through the protection of surface water and groundwater, as well as eliminating the need for using preemergence herbicides. Either increase or decreases have been reported for crop yields when the crop residues remain on soil surface. No-till system has been reported to increase the presence of certain difficult to control weeds. Therefore, the aim of this study was to investigate the effect of tillage systems and cover crops on weed control and corn yield.
Experiment was carried out as split plot based on randomized complete block design with three replications at the Bu-Ali Sina University in growing season of 2011. Tillage with moldboard, tillage with chisel (minimum tillage), and no tillage were considered as main plots and two cover crops, winter vetch and chicklingpea, chemical weed control and weed-infest treatment (control) were considered as sub-plots. Cover crops were cultivated in late March 2011. In early June 2011, cover crops were harvested and were spread over the soil surface. The Plot size was 22.50 m-2. Five rows were in each plot with 75 cm intervals among rows and 18 cm among seedlings. 2 square were picked in the three central rows of each plot in order to determine the yield and yield components. From each plot three quadrants (1×1 m)randomly were picked and weeds and cover crops was separated. All samples were dried at 72 ° C for 48 hours and then were weighed. Data were analyzed using SAS software. Wherever the F test showed significant effect for a source of variance, the differences among treatments were compared by LSD test at the 0.05 level of significance.
Analysis of variance showed that the effects of tillage systems and weed control methods were significant on all traits, except number of seed per ear. Also, the interaction effect of them had significant effect on number of grain row/ear and grain yield. The highest grain yield (1271 g m-2) was observed at combined treatment of winter vetch cover crop and moldboard tillage. This treatment had no significant difference with combined treatments of cover crops and tillage with chisel. In comparison with winter vetch cover crop and conventional tillage treatment, the lowest grain yield by 45% reduction was recorded at weed infested and no tillage treatment. Also, the effects of tillage systems and weed control methods and their interaction were significant on weed density and biomass. Maximum weed density and biomass (60 plant m-2 and 335 g m-2) were belonged to weed-infested treatment under no tillage system. The lowest values for weed density and biomass with reduction of 62 and 53%, respectively, were observed at combined treatment of chicklingpea cover crop and minimum tillage. Chicklingpea and winter vetch cover crops due to rapid establishment and growth capacity are more suitable for weed control. Cover crops can affect weed establishment through effects on the radiation and chemical environment of weed and inhibit weed emergence by physically impeding the progress of seedlings from accessing light as well as by releasing phytotoxins that inhibit seedling growth. Minimum tillage is often cause changes in of weed flora and their population, and this is one of the methods for integrated weed management. In general, using winter vetch and chicklingpea as a cover crop and tillage with chisel suppressed about 50-60% weeds and increase corn yield which is effective step towards achieving sustainable agriculture.